I don’t know why but DirectAdmin still rolls out with PHP 5.3 which was released in June 2009. It is now June 2014, how about an upgrade?
You might not want to jump to PHP 5.5 because it deprecates a bunch of the ‘old way’ of connecting to mySQL.
But is it safe to move to 5.4? If you want to find out and are running DirectAdmin, you can update with custom build like this:
cd /usr/local/directadmin/custombuild ./build update ./build set php5_ver 5.4 ./build php n
Is your system still going to work? Guess you will have to upgrade and find out.
If you had installed any extensions that you compiled, odds are good they will no longer function because they were compiled for another version.
To quickly fix memcache I just did the following to commands
pecl uninstall memcache
pecl install memcache